A view is a sequence adaptor delivering an altered presentation of
one or more underlying sequences. Views are lazy, meaning that their
elements are only computed on demand. Similarly to the short-circuit
logical operations and eval_if, views make it possible to avoid
premature errors and inefficiencies from computations whose results
will never be used. When approached with views in mind, many
algorithmic problems can be solved in a simpler, more conceptually
precise, more expressive way.